Phenalenyl-ruthenium synergism for effectual catalytic transformations of primary amines to amides

Abstract

The synthesis of amides holds great promise owing to their impeccable contributions as building blocks for highly valued functional derivatives. Herein, we disclose the design, synthesis and crystal structure of a mixed-ligand ruthenium(II) complex, [Ru(η⁶-Cym)(O,O-PLY)Cl], (1) where Cym = 1-isopropyl-4-methyl-benzene and O,O-PLY = deprotonated form of 9-hydroxy phenalenone (HO,O-PLY). The complex catalyzes the aerobic oxidation of various primary amines (RCH₂NH₂) to value-added amides (RCONH₂) with excellent selectivity and efficiency under relatively mild conditions with common organic functional group tolerance. Structural, electrochemical, spectroscopic, and computational studies substantiate that the synergism between the redox-active ruthenium and π-Lewis acidic PLY moieties facilitate the catalytic oxidation of amines to amides. Additionally, the isolation and characterization of key intermediates during catalysis confirm two successive dehydrogenation steps leading to nitrile, which subsequently transform to the desired amide through hydration. The present synthetic approach is also extended to substitution-dependent tuning at PLY to tune the electronic nature of 1 and to assess substituent-mediated catalytic performance. The effect of substitution at the PLY moiety (5^th position) leads to structural isomers, which were further evaluated for the catalytic transformations of amine to amides under similar reaction conditions.